HACKING

zunkfs is a "content-addressable-filesystem." Ie, everything in it is kept via SHA1 hashes.  And it's got some light encryption in it too.

Files and directories are described by a "disk directory entry" (disk_dentry or ddent for short.) A ddent has the following stuff in it:

- name of the file/directory (upto 196 chars)
- 20 byte, SHA1 hash desribing the "root chunk" [1] of the file.
- 20 byte, SHA1 hash desribing the "secret chunk" [2] of the file.
- file/directory size (bytes or # of entries)
- "mode" (rwx, file or directory)
- create time (in seconds)
- modify time (in seconds)

The fs itself is described by the ddent that defines the / directory.
All entries and divided up into 64k-sized chunks, and are stored in
a tree structure. The tree is dynamically expanded to fit all chunks
needed for the file. Internal nodes of the tree are also chunks, which contain
lists of 20-byte hashes of other chunks.

       [ root chunk ]
        /    |      \
 [ leaf 1 ] [leaf 2] [leaf 3]

In the case of files, leaf chunks contain file data. For directories, leaf chunks contain arrays of ddents.

[1] The "root chunk" of the file contains the root chunk of a chunk tree which contains the files data.

[2] The "secret chunk" is used to do simple XOR-based mangling of all chunks.
All chunks in a files chunk tree are mangled with this XOR. The hash that is stored is that of the final XORed data. When a file or directory is created, a new random chunk is also created to be the secret chunk for that ddent.

At the moment, chunks are stored a ".chunks" directory in the current working directory. I've verified that I can copy some files and create directories within a zunkfs mount. Created files will match the expected SHA1 hash of the original. And they are preserved accross remounts.

--- random thoughts captured from drze ---

try running: zunkfs-list-ddents in a zunkfs directory

zunkfs-add-ddents lets you add stuff from somebody else's zunkfs
If you were to create an empty zunkfs then do 
  $ zunkfs-add-ddent file <digest> <secret digest> <size> <name>
zunkfs-list-ddents lists the <digest> <secret digest> <mode> <size> <ctime> <mtime> <name>
If we were all connected to some shared chunk-db btu we've got our own zunkfs roots and I want a file that you have got you just give me three things:
  1) digest
  2) secret digest
  3) size
and from that, I can get at that file (same thing applies to directories)

zunkfs-list-ddents --car